The entry of HIV-1 into cells involves binding of the viral envelope (env) protein to CD4 followed by interaction with one of several coreceptors (reviewed in E. A. Berger, 1997, AIDS, 11:S3-S16; Broder et al., 1997, J. Leukocyte Biol., 62:20-29; Doms et al., 1997, Virology, 235:279-190; and Moore et al., 1997, Curr. Opinion Immunol., 9:551-562). Binding of the env protein to the appropriate coreceptor is thought to trigger conformational changes in env that mediate fusion between the viral membrane and the host cell membrane. The CCR5 and CXCR4 chemokine receptors have been identified as major HIV-1 coreceptors in that all HIV-1 strains examined to date use one or both of these molecules as second receptors. CCR5 supports infection by R5 (M-tropic) virus strains, while CXCR4 supports infection by X4 (T-tropic) virus isolates (Alkhatib et al., 1996, Science, 272:1955-1958; Berger et al., 1998, Nature, 391:240; Choe et al., 1996, Cell, 85:1135-1148; Deng et al., 1996, Nature, 381:661-666; Doranz et al., 1996, Cell, 85:1149-1158; Dragic et al., 1996, Nature, 381:667-673; and Feng et al., 1996, Science, 272:872-877). R5-X4 (dual-tropic) viral env proteins can, in conjunction with CD4, use either CCR5 or CXCR4 for cellular entry. The differential utilization of CCR5 and CXCR4 by HIV strains, coupled with their expression patterns in CD4 positive cells largely explains viral tropism at the level of entry.
In addition to CCR5 and CXCR4, a number of other chemokine and orphan seven transmembrane domain receptors have been shown to function as coreceptors for one or more virus strains in vitro, including CCR2b, CCR3, CCR8, CX3CR1, GPR1, GPR 15, STRL33, US28, and ChemR23 (Choe et al., 1996, Cell 85:1135-1148; Deng et al., 1997, Nature 388:296-300; Doranz et al., 1996, Cell 85:1149-1158; Farzan et al., 1997, J. Exp. Med. 186:405-411; Liao et al., 1997, J. Exp. Med. 195:2015-2023; Pleskoff et al., 1997, Science 276:1874-1878; Reeves et al., 1997, Virology 231:120-134; Rucker et al., 1997, J. Virol. 71:8999-9007). In general, these alternative coreceptors support virus infection less efficiently than either CCR5 or CXCR4. However, use of alternative coreceptors may help explain certain facets of HIV-1 tropism and pathogenesis in vivo. For example, neurologic disease is a serious and relatively frequent consequence of HIV-1 infection, with microglia being the primary targets of virus infection in the central nervous system (Bagasra et al., 1996, AIDS, 10:573-585; Sharer et al., 1992, J. Neuropath. Exp. Neurol., 51:3-11; Wiley et al., 1986, Proc. Natl. Acad. Sci., USA, 83:7089-7093). Microglia express both CCR3 and CCR5 and it has been suggested that utilization of CCR3 by a virus strain may correlate with neurotropism (He et al., 1997, Nature, 385:645-649).
The identification of additional coreceptors for the HIV virus would provide an important tool for investigating and controlling HIV infection.
In one aspect of the invention, the invention relates to a recombinant eukaryotic cell transformed with a polynucleotide encoding an APJ polypeptide and/or a polynucleotide encoding a CD4 polypeptide, wherein the cell coexpresses APJ and CD4 polypeptides.
The invention also relates to an antibody which specifically binds to an extracellular domain of APJ, wherein the antibody inhibits HIV infection of a target cell that coexpresses APJ and CD4 polypeptides or wherein the antibody inhibits membrane fusion between a first cell coexpressing APJ and CD4 polypeptides and a second cell expressing an HIV env protein.
The invention also relates to a substantially purified peptide fragment of APJ, wherein the peptide inhibits HIV infection of a target cell that coexpresses APJ and CD4 polypeptides or wherein the peptide inhibits cell fusion between a first cell coexpressing APJ and CD4 polypeptides and a second cell expressing an HIV env protein.
In another aspect of the invention the invention relates to methods for identifying compounds that modulate the interaction between an HIV virus and an APJ receptor.
The invention also relates to a method of inhibiting HIV infection of a target cell expressing an APJ and CD4 polypeptides comprising contacting the target cell with an effective amount of an APJ binding or blocking agent.
The invention also relates to a method of treating a subject having or at risk of having an HIV infection or related disorder, comprising administering a therapeutically effective amount of an anti-APJ antibody to the subject.